If I bought one from say ebay at the link below, do I just plug it in and start mining?http://www.ebay.com/itm/ASICMiner-USB-Block-Erupter-Bitcoin-Miner-In-Hand-/111240213659?pt=LH_DefaultDomain_0&hash=item19e66ef49b
A good estimate is around 0.01 BTC over the next 6 months or so, at which point electricity costs will make it unprofitable. Since it will cost about 0.07 BTC, you will never make a profit, but it will be a good learning experience.